Bioflavonoids are naturally occurring plant pigments in fruits and vegetables which humans consume daily in gram quantities. These compounds possess estrogenic and anti-estrogenic properties and therefore, ingested bioflavonoids may have significant impact on human reproduction. Equol and daidzein are isoflavonoids (phytoestrogens) which bind to the estrogen receptor (ER), and consumption of these substances causes reduced fertility (Clover Disease) in sheep. Isoflavonoids may also possess carcinogenic or teratogenic activity related to these estrogenic properties as is the case for "environmentally" derived DES. Conversely, flavonoids (luteolin and quercetin) and their metabolites (methyl p-hydroxyphenyllactate; MeHPLA) possess antiestrogenic activity and this is associated with their ability to bind to nuclear type II sites (not the ER) with high affinity and inhibit normal (rat uterus) and malignant (breast cancer cells, mammary tumor growth in mice) cell growth and proliferation. These anti-estrogenic properties suggest that certain dietary bioflavonoids and/or their metabolites may also alter reproductive function and possess anti-carcinogenic or anti-teratogenic activity. The mechanisms by which environmentally derived dietary bioflavonoids modulate estrogen target cell growth and proliferation are not well understood. The overall goal of this proposal is to explore the basic underlying mechanisms by which estrogenic and anti-estrogenic bioflavonoids and/or their metabolites modify estrogen target cell function. Tritiated isoflavonoids ([3H]equol, [3H]daidzein) and bioflavonoids ([3H]luteolin and [3H]quercetin) will be administered (parenterally and orally) to rats and the form (parent compound and/or metabolites) of the compound present in serum, liver and the rat uterus (cytosol, nuclei, mitochondria and microsomal fractions) responsible for the observed estrogenic or anti-estrogenic activity will be identified. Potentially active metabolites will be purchased or synthesized. These metabolites and the parent compounds will be directly evaluated for estrogenic and anti-estrogenic activity in vitro (MCF-7 human breast cancer cells) and also following oral or parenteral administration in vivo (rat uterus) . Binding interactions of these compounds with ER and type 11 sites will be evaluated and correlated to treatment effects on progesterone receptor (PgR) induction, MeHPLA esterase activity and the regulation (stimulation or inhibition) of normal (rat uterus) and malignant (MCF-7 cells) cell proliferation. These studies will identify the active form(s) of bioflavonoids in target cells and define specific biochemical sites at which these dietary estrogens, antiestrogens and/or metabolites interact to alter estrogen target cell proliferation and reproductive function.